Bottling lines usually include (see Unexamined German Patent 196 24 552, for example) inspection systems for empty bottles to be filled. Bottles positioned on a conveyor belt pass through individual inspection devices or modules one after the other to detect certain defects (foreign bodies, residual fluid, damage, material stresses, etc.) in the bottles, so that damaged bottles can be sorted out from the bottling lines.
In particular, the individual inspection modules may each include a camera which records a single image of a glass bottle as it is conveyed past the camera, where the imaging lens of the camera is selected and arranged in such a way that it is also possible to perform an inspection of a side wall or bottom of the container, for example,
An image analyzing system connected to such a camera using an image processing program that runs on a computer analyzes the individual image data thus compiled and optionally delivers an error signal to a reject device so that a bottle found to be defective is automatically sorted out from the conveyor belt as a reject.
The image analysis is performed with certain parameter settings of the image analysis program which may be set or altered automatically on manually by an operating person during the analysis or during pauses in the analysis.
These inspection devices may have response characteristics that vary over time, however, so it is necessary to check all functions at certain intervals and optionally perform a suitable readjustment of the individual inspection devices.
Test bottles are usually added either automatically or by hand into the stream of bottles after having been prepared so that they are detected as defective if the inspection modules all function correctly. If these test bottles are not detected as defective, the respective inspection module is faulty, i.e., it is defective or out of adjustment.
This may be due to soiling of the lens or failure of individual components of the electronic detection system or the parameter settings of the image analysis program may be out of adjustment. Such inspection systems are known, for example, from German Utility Model No. 299 10 452.4, which discloses a generic method and a generic device. In this regard, reference is also made to the publications German Patent 196 46 694 A1 and German Patent 43 02 656 C2.
Test bottles may undergo negative changes in their original properties over a period of time due to frequent use. Furthermore, the certainty of detecting test bottles may depend on their random rotational position on the conveyor belt of the inspection machine. The results that can be achieved with the known test bottles are therefore poorly reproducible in principle and are not adequately comparable. These are only simple tests of detected versus not detected which do not allow any qualitative conclusions.
German Patent 2 166 235 and German Patent Application 33 30 817 A1 describe the fact that as an alternative it is not absolutely necessary to introduce prepared test bottles into the path of the beam of the inspection modules, but instead other artificial sources of error may also be introduced in order to check on correct functioning of the inspection process.
However, there is the possibility that in practice the program parameters of the image analysis programs might be partially adjusted in particular by inadequately trained operating personnel, so that the sensitivity of detection of errors is reduced beyond an unacceptable extent. Consequently, there may be cases in which defects in bottles such as abrasion rings in the outer base area of the bottles have a lower probability of being detected, so this reduces the defective bottle reject rate.